Gasification of Black Liquor with the Addition of Secondary Sludge
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The effects of secondary sludge addition on black liquor gasification were studied. Additions of 0, 5, 10, and 15% secondary sludge solids to hardwood black liquor solids were considered. Gasification temperatures were 700 and 900°C. Residence times were 0.2, 0.7, and 1.2 seconds. Gasification was performed in a laminar entrained flow reactor. Although both amount and rate of organic carbon conversion increased with temperature, the percentage of sludge addition did not affect percent of feed carbon recovered as organic carbon. Isobutyl and ethyl mercaptan, as well as carbon disulfide, were not produced in reportable quantities. Recoveries were expressed on a percentage-of-feed-element basis. Recovery of sulfur in char was higher for the 100/0 (black liquor/secondary sludge) feed than for the 85/15 feed. Recoveries of H2S were higher for purer (less sludge added) feed stocks for all experiments except those performed 900°C/1.2 seconds residence time. Recoveries of methyl mercaptan, n-propyl mercaptan, carbon disulfide, and ammonia were relatively independent of sludge addition. Recoveries in char of magnesium, vanadium, and aluminum were higher for the 85/15 feed stock.